I'm constantly running into issues with having hierarchical data stored in an RDBMS. To me, it seems like an indicator that it's the wrong tool for the job. The "job" is to store a hierarchical survey and the results from multiple respondents for a given date range. The survey questions may slightly vary from one date range to the next. An RDBMS seems suitable for storing the results. However, for the survey itself, since it's a tree-structure and ordering matters, seems better suited for XML.
Would it be considered bad practice to store the survey tree in XML and the actual results in an RDBMS? If not, then how would I relate an XML element to a table row? E.g. a survey question to a respondent's answer.